Two types of marine A/C systems Tom...
A marine a/c pro posted this on another site...I thought it worth adding to my collection of useful information and saved it...There are basically two types of marine a/c systems: self contained units and split systems. Usually, the size of your boat determines which type you have. A self contained unit has the "air handler" (blower) attached to the same chassie as the compressor and evaporator. The output side of the blower is attached to some type of plenum (usually a box type device) and then ducted to the appropriate areas of the cabin. The intake side of the blower(return air) is attached directly to the evaporator coil.This is the type that "strongly advise isolating from the bilge and engine." Many boat manufactures just drop this type of unit into a convenient spot such as under the v-berth or in the side wall of the aft-cab just ahead of the engine compartmen's fire wall. In fact, in both applications, they simply cut a hole in the wall and plunk a grill in. They don't make a physical connection to the grill. The assumption is that the unit will pull most of the air from the grill (cabin).Not truly the case. Some of the "return air" is pulled from the side wall along whatever side the unit is mounted on. If the head is on the side wall and someone does a stinker, it's possable the unit will pull that air in and circulate it through the cabin. :-( If the unit is under the v-berth and there is a bilge area under or just aft, you can pull any smells from there as well.In larger boats, a split systems is used. The compressor, condensor unit is in the engine room or bilge and refrigerant is piped to a air handler/evaporator coil/condensate drain pan that is in the cabin. With these types of systems, the "air-handeler" will have an intake somewere in the cabin and a plenum to distribute the air. In both types, the intake of the air-handler is almost never piped directly into the cabin. These systems CAN pull air from all over except the engine room.Split systems have the condensate drain pan attached directly below the evaporator coil in the intake side of the system. Self- contained systems have the condensate pan as part of the chassie. Both are notorious for mold and other gross stuff. If these pans don't drain completely and many don't, the stagnent water will start to smell like a holding tank and will be worse when the unit turns on. Don't forget about the filters on the intake side. They should be cleaned/replaced at least 2 times during the boating season. More if you are in dusty conditons.Never run an A/C unit without filters attached. If at all possible, make sure the filter is attached directly to the evaporator coil and not just the back of the grill in the cabin wall. The idea here is that a filter is much easier to clean than the coil. If however, your coil is very dirty, that will be a source of odor as well. They can be cleaned with any air-conditioning coil cleaner available in most hardware stores. PLEASE FOLLOW DIRECTIONS ON LABEL. All coil cleaners contain a mild acid solution and all cleaning solutions must be followed with a water wash. If your drain goes into a sump, make sure the cleaner is safe for plastic and rubber (most are). Clean coils not only smell better but increase/maintain the efficiency of your A/C unit.